This invention relates generally to a method of controlling hydraulically actuated valves, and more particularly to a method of reducing impact velocities for hydraulically actuated exhaust and intake valves of an engine.
In engines utilizing mechanically activated valves, such as gas exchange valves, a cam drives a valve member within the valve to move between a closed position and an open position. Thus, for a mechanically controlled exhaust valve, rotation of a cam moves the exhaust valve member from its closed position to its open position, and vice versa, at a speed corresponding to the cam profile and its rotation rate. In engines such as these, the impact velocity of the valve member closing a respective valve seat can be on the order of tens of centimeters per second. While these impact velocities are acceptable, there is a trend in industry to move away from cam actuation toward electronic control in order to control events independent of engine speed and crank angle.
In response to this trend, the use of hydraulically actuated electronically controlled gas exchange valves, such as exhaust and intake valves, has been on the rise. For instance, U.S. Pat. No. 5,255,641 issued to Schechter on Oct. 26, 1993, discloses an engine having hydraulically controlled intake and exhaust valves. In these valves, the impact velocity of the hydraulically actuated valve member closing its respective valve seat can be as much as an order of magnitude or more greater than that for a mechanically actuated valve member. High impact velocities, such as those produced in some hydraulically actuated valves, can fatigue the valve stem and wear out the seat area, which can lead to a reduction in the effective life of the gas exchange valve member and its respective valve seating surface.
One prior method of reducing impact velocities for hydraulically actuated gas exchange valve members included placing a flow restriction in the drain of the valve actuator. However, the presence of a flow restriction causes the velocity of the valve member to slow over the entire travel distance between its open position and its closed position. While this strategy can reduce the impact velocity, the valve closing event is lengthened, possibly to the point of interfering with other engine events. Therefore, a method of reducing the impact velocity that does not significantly lengthen the duration of the valve closing event would find particular application with hydraulically actuated gas exchange valves.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, an improvement for a hydraulically actuated valve having a valve member operably coupled to a hydraulic valve actuator includes a hydraulic pulse generator fluidly connected to the hydraulic valve actuator. The hydraulic pulse generator is capable of directing a hydraulic pulse toward the valve member as the valve member is moving from a first position toward a second position.
In another aspect of the present invention, an engine includes an electronic control module having a means for determining when a valve member of a hydraulically actuated valve is at a predetermined location between a first position and a second position. Also provided is a means for directing a hydraulic pulse toward the hydraulically actuated valve when the valve member is approaching the second position, wherein the magnitude of the hydraulic pulse is insufficient to reverse a movement direction of the valve member.
In yet another aspect of the present invention, a method of controlling hydraulically actuated valves includes providing a hydraulically controlled valve that has a valve member that is movably positioned in a valve body, wherein the valve member is movable between a first position and a second position and provides a hydraulic surface. Movement of the valve member toward the second position is slowed, at least in part by directing a hydraulic pulse toward the valve member when the valve member is moving toward the second position.